N-methyl-2-pyrrolidone or 1-methyl-2-pyrrolidone (NMP) is a versatile and highly useful chemical which finds large and diverse applications in a wide variety of end uses from electrochemical to petrochemical industries. NMP exhibits higher thermal stability; nontoxicity and having low viscosity which makes it highly useful to be used in chemical synthesis and for the preparation of semiconductors. It is colorless in nature or may be of yellow color depending on the level of impurity present in it. NMP belongs to a class of dipolar aprotic solvents like dimethyl formamide and dimethyl sulphoxide. Due to non-volatile nature and ability to dissolve diverse chemicals, NMP is used as solvent for extracting and recovering certain high value hydrocarbons during petrochemical processing e.g., in the recovery of 1,3-butadiene from cracked C4 stream, and aromatics (BTX) from naphtha/pyrolysis gasoline etc. The NMP extracted 1,3-butadiene from cracked C4 stream from stream crackers is so far the main source of 1,3-butadiene for polymer industries. The good solvency property of NMP also makes it very useful in the polymer industries as a solvent for surface treatment of textiles, resins, and metal coated plastics or as a paint stripper. It is utilized as a solvent in the commercial preparation of polyphenylene sulfide. In the pharmaceutical industry, N-methyl-2-pyrrolidone is used in the formulation for drugs by both oral and transdermal delivery routes.
It is pertinent to mention that the industrial preparation of NMP is predominantly carried out by reaction of gamma-butyrolactone (GBL) with mono methylamine (MMA) in a tubular reactor, e.g. a shaft reactor, at temperature from 200 to 350° C. and super atmospheric pressure, e.g. about 10 MPa (Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, Vol. A22, pages 458 to 459 (1993).
There are several other processes for the synthesis of NMP from gamma-butyrolactone with mono methylamine (MMA) as a starting material.
Reference may be made to several patents (JP7221420, JP7400259, JP7420585, JP7642107) Mitsubishi Chemical Industries Co. Ltd. of Japan described continuous processes for the synthesis of NMP using GBL and MMA as starting materials. The production of NMP was carried out by reactions with high molar ratios between water and shot GBL (typically ranging between 3 and 4 moles of water for each mole of GBL) and by the presence of great amounts of MMA (typically with molar ratios ranging between 1.4-3 moles of MMA per mole of GBL).
Reference may be made to an Indian patent application number: 4/MUM/2007 (publication no. 39/2008) assigned to Balaji Amines Limited discloses a process for the production of NMP from gamma-butyrolactone (GBL) and mono methyl amine (MMA) at a desired molar ratio in a series of reactors operated at temperatures in the range of 200 to 300° C. and pressures in the range of 30 to 90 atmospheric for a residence time of 15 to 150 minutes. NMP thus obtained reported to purity of not less than 99.7% and yield of greater than 90%.
Reference may be made to the U.S. Pat. No. 6,348,601 B2 assigned to BASF discloses a method for N-Methyl-2-pyrrolidone (NMP) production by preparing a mixture comprising monomethylamine, dimethylamine and trimethylamine in a first step by reacting ammonia with methanol at elevated temperature in the range of 300 to 500° C. and pressure in the range of 1500 to 3000 kPa in the presence of a solid acid catalyst and hydrogen, followed by separating off the ammonia and then reacting the mixture comprising methylamines with gamma-butyrolactone (GBL) in a molar ratio of monomethylamine to GBL in the range of 1.05 to 1.5 at temperature 230 to 270° C. and pressure 50 to 150 bar in a second step for a residence time of 2 to 4 hrs. The process elaborated yields NMP at a selectivity of 95% or more at the conversion of GBL of 99%.
Reference may be made to the U.S. Pat. No. 6,248,902B1 assigned to Pantochim S.A., describes a process for the production of N-methyl-pyrrolidone obtained by reaction of gamma-butyrolactone and monomethylamine, wherein the synthesis is carried out by a continuous non-catalytic process in liquid phase, via three distinct reaction stages connected in series. Three reactors operated in the range of temperature 150 to 310° C. and pressure 30 to 90 atmospheric and residence time of 5 to 180 minutes which gives a conversion of GBL of more than 98% with selectivity to NMP 95% or more.
Reference may be made to the U.S. Pat. No. 6,987,191B1 assigned to BASF also discloses a process for the production of N-methyl pyrrolidone using gamma-butyrolactone and mixed methylamines as starting materials, in a continuous process, in such operating conditions as to allow the production of high purity N-methyl-2-pyrrolidone in high yields. The process also consists of three stages in series at operating temperature in the range of 150 to 310° C. and pressure 40 to 100 atmospheric for residence time 15 to 180 minutes. The conversion and selectivity of GBL and NMP reported to be of more than 98% and 95% respectively.
Reference may be made to the Chem. abstracts 124:145893 (CN-A-11046 35) describes the synthesis of NMP by reaction of GBL with MMA at 220 to 290° C. and 26 MPa (260 bar). The batch wise reaction of a mixture of GBL, 30% strength aqueous MMA and water in a weight ratio of 1:1.4:5.6 at 280° C. and 6 MPa (60 bar) gives NMP in a yield of 97%. The above weight ratio corresponds to a molar ratio of GBL:MMA:H2O of 1:1.2:26.7 (without taking the water in the MMA solution into account) or a molar ratio of 1:1.2:31.5 (when the water in the MMA solution is taken into account).
Reference may be made to the Chem. abstracts 129:67694 (JP-A2-10158238) relates to the reaction of GBL with from 1.03 to 1.50 molar equivalents of MMA in the presence of from 1.0 to 2.9 molar equivalents of water at from 250 to 300° C. The batch wise reaction of GBL with MMA and water in a molar ratio of 1:1.1:1 at 280° C. for 1 hour gives NMP in a yield of 99.9%.
Reference may be made to the Derwent abstract 1998-607722, Chem. Abstracts 134:178463 (RO-B1-113640) relate to a process for the continuous preparation of NMP in the liquid phase in a two stage procedure. The reaction conditions in the first stage are: molar ratio of GBL, MMA and water: 1:1.2:2.1, temperature of 150 to 170° C. and pressure of 90 to 100 bar. The reaction conditions in the second stage are: 280 to 290° C. and 90 to 100 bar.
Reference may be made to the Chem. abstract 82:139947 (JP-B4-49 020 585) describes the reaction of one part of GBL With two parts of monomethylamine and from 2 to 4 parts of water (molar ratio of 1:5.5:9.6-19.1) at 250° C. for 2 hours to give NMP in a yield of 99%. The temperature range for the reaction is generally from 200 to 300° C., in particular from 230 to 300° C.
Reference may be made to the Chem. abstract 87:5802 (JP-A2-49 041364) discloses the reaction of GBL with monomethylamine and water as a 1:1.4:4 mixture (molar ratio of 1:3.9:19.1) at 250° C. and from 44 to 49 bar.
Reference may be made to the U.S. Pat. No. 7,227,029B2 assigned to BASF describes a process for the continuous preparation of N-methyl-2-pyrrolidone (NMP) by reacting gamma-butyrolactone (GBL) with monomethylamine (MMA) in the liquid Phase, wherein GBL and MMA are used in a molar ratio of from 1:1.08 to 1:2 and the reaction is carried out at from 320 to 380° C. and an absolute pressure of from 70 to 120 bar at a space velocity of 1.4 kg/h of GBL per unit volume of reactor. The process yields NMP at a selectivity of more than 98% under conversion of GBL of more than 98%. The process claims use of an upright tube reactor in which the monomethylamine and the GBL are fed separately at the bottom of the reactor via a two fluid injector provided the feed mixture contains less than 10% by Weight of Water.
Reference may be made to the U.S. Pat. No. 2,964,535 assigned to Monsanto relates to a process for purifying NMP by treatment with an alkali metal hydroxide in aqueous solution and subsequent distillation.
The thermal processes at liquid phase although lead to high NMP yield but they suffer from the following disadvantages:                a. High pressure requirement to carry out the reaction in the liquid phase involves high engineering outlay associated with high capital and operating costs        b. High corrosion rate of aqueous methyl amine solution at high temperature and high pressure reduce the life of equipments and thus increase the capex and opex of the plant        c. Plurality of reaction stages to get the high space time yield of NMP is associated with high capital and operating costs        
The processes described by Mitsubishi is also disadvantageous in terms of the high costs involved with the separation of excess MMA and its recovery and with the separation of the water forwarded to the reaction to which synthesis water adds up (one mole of water for each mole of reacted GBL).
To avoid the drawbacks associated with the continuous reaction in the presence of excess MMA and water, alternative methodologies have been proposed and these are based on the employment of catalysts.
Reference may be made to the German Patent No. 2,159,858 owned by Mobil Oil a synthesis with GBL and MMA in the presence of 13X type Zeolites is described.
Reference may be made to the German Patent No. 4,203,527 owned by AKZO, a synthesis involving GBL, MMA and steam in the gas phase and at a temperature of 275° C. on a NaX type Zeolite is described.
The above mentioned processes did not succeed in being applied industrially, as the employment of the mentioned catalyst subject to regenerations is disadvantageous in terms of the economic balance of the process as compared with non-catalytic processes.
Thus, the overall drawbacks of the prior art processes to produce NMP are:
a. High pressure requirement to carry out the reaction in the liquid phase involves high engineering outlay associated with high capital and operating costs
b. High corrosion rate of aqueous methyl amine solution at high temperature and high pressure reduce the life of equipments and thus increase the capex and opex of the plant
c. Plurality of reaction stages to get the high space time yield of NMP is associated with high capital and operating costs.
d. the high costs involved with the separation of excess MMA and its recovery and with the separation of the MMA.
The need of the present invention from industrial outlook is therefore of utmost importance to produce NMP from GBL and MMA preferably in aqueous form in a typical molar ratio GBL to MMA at a milder condition than that as per the prior art of literatures, in presence of a catalyst which does not need to regenerate frequently. Another potential aspect of the present invention is the low cost of separation of the product as NMP is produced at a very high selectivity ≥99% at the conversion of GBL ≥99%.